Regular comparison operators (i.e. == and !=) only apply to value
channel; when used with missing values they always result in NA.
By contrast,
the multichannel comparison operators %==% and %!=% compare BOTH the
value and missing reason channels of a variable. Multichannel equality
%==% operates identically to regular == when both operands are values,
but will return FALSE instead of NA when one is missing. When both values
being compared with %==% are missing values, their missing reasons are
compared. Multichannel comparison operators always return boolean values,
never NA